mating systems Flashcards
monogamy
1 female, 1 male
mate guarding
mate assistance
female enforced
polygyny
1 male, 1+ females
female defense
resource defense
scramble competition lek
polyandry
1 female, 1+ males
resource defense
male defense
2 main factors to consider?
male and female dispersion in space and time
-how easy is it to access mates?
patterns of desertion by either sex
- depends on cost and benefits of parental care
Factors governing the diversity of mating systems
Mating systems WITHOUT male care
Mating systems WITH male care
If males do not provide parental care
Assumption: male reprod. success limited by access to females
Prediction: males can compete for females directly or indirectly
Low chance for Polygamy
Resources (food, nest sites) and/or mates are evenly distributed relative to defended territorie
High chance for Polygamy
Patchy resource distributions enable some individuals to ‘grab more than their fair share’
Operational Sex Ratio of 1:1
Ratio of reproductive males to reproductive females
If all females breed in synchrony and the real sex ratio is 1:1.
common toad mating system
explosive breeders
– Breed only for a few nights
– Females synchronous
– More even (1:1) OSR
– Low variance in male success
– Resource defense not feasible
– Scramble competition
bullfrog mating system
prolonged breeders
– Breed over extended period
– Females asynchronous
– Male biased OSR
– High variance in male success
– Resource defense feasible
– Resource defense polygyny
Experimental evidence for Emlen and Oring (1977)
Female distributions governed by food
- In high food areas, female ranges are small and overlapping
Males follow to high female sites
Mammalian mating systems depend on
resource and female dispersion patterns
Polygyny: females have smaller ranges than male territory
Monogamy: females have larger ranges than male territory
leks and choruses
Agreggations of males on small mating territories
….each male displays for choosy females
mating is strongly skewed towards a few males
lek paradox
Since females usually mate with one male,
why do other males bother to come to the lek at all?
And, if one male gets most matings, why is there still variance in male traits?
lek paradox hypotheses
hotspot (Males settle on areas where
female encounter rate is high)
hot shot (Males cluster at leks to parasitize better signallers)
Males aggregate to reduce predation risks
Males aggregate to amplify signal and increase female attraction
Females prefer leks because they facilitate female choice
Why are males monogamous?
Monogamous bird couples leave more descendents fi they share parental care
- familiarity improves parental performance
- older individuals have more experience
Monogamy exists because of low opportunities to be polygynous
- strong competition among males (hard to get 2nd mate)
- females likely suffer in polygyny because loss of help
Female enforced monogamy hypothesis
Monogamy is not adaptive for males but forced into it
Male burying beetles
why is social monogamy relatively rare in mammals but common in birds
Eggs develop internally in mammals, externally in birds
Differences in constraints and costs between sexes in parental care
why does social monogamy not guarantee genetic monogamy
Extra pair copulations by both genders are common…
- males benefit: paternity
- females benefit: fertilisation success, genetic diversity, good genes
DNA technology to assign parentage
microsatellites
Useful for assigning parentage and kinship because:
- highly polymorphic
- inherited in a Mendelian fashion
polygyny threshold model
females may choose polygyny
costs of sharing a male’s help with parental care
outweighed by the benefits of gaining access to good resource
what does polygyny threshold model assume
ideal free distributin
3 broad themes in mating system diversity
Life history constraints
Ecological factors
Social conflicts
